In fiber optic systems, various methods have been previously developed for switching optical signals between fiber optic cables. These previously developed methods can be classified into three categories: electrical, solid-state, and mechanical.
Electrical switches convert an optical signal to an electrical signal and then switch the electrical signal by conventional switching techniques. Electrical switches then convert the electrical signal back into an optical signal. Electrical switching of optical signals is faster then when using existing mechanical switches, but is also significantly more expensive. Additionally, electrical switching of optical signals is bandwidth limited, i.e., a converted electrical signal cannot "carry" all of the information in an optical signal. This limitation prevents electrical switching of optical signals from utilizing the full optical bandwidth available with fiber optics, and severely limits the advantages available when using fiber optics.
Solid-state optical signal switches typically use titanium diffused lithium niobate devices. Solid-state switches have fast switching speeds, less than one nanosecond, and the same bandwidth capacity as fiber optics. Solid-state switches, however, cost 30 to 100 times more than existing mechanical switches and have insertion losses exceeding 20 times those for existing mechanical switches.
Previously developed mechanical switches for switching optical signals are typically lower in cost than electrical or solid-state optical switches, provide low insertion loss, and are compatible with the bandwidth of fiber optics. Currently available optical mechanical switches, however, are relatively slow, with switching speeds of approximately 5 to 50 ms.
The actuators used in some existing mechanical switches result in their slow switching speed. Previously developed optical mechanical switches typically move mirrors or prisms or rotate the fiber to change the signal path for an optical signal. Alternatively, existing mechanical switches change a signal's path by moving the input fiber itself to align with the desired output fiber. Both of these techniques require moving large masses (mirrors or prisms) in a minimum time period. Existing optical mechanical switches may use solenoids and motors or piezo-electric transducers as the actuators.
Recent developments in network systems, such as SONET and asynchronous transfer mode (ATM) packet switching systems, require optical signal switching speeds of 10 .mu.s or less. This speed is approximately 1,000 times faster than available through previously developed optical mechanical switches. Therefore, in order to obtain the benefits of fiber optic networks, more expensive electrical or solid-state switches must be used. Additionally, electrical and solid-state fiber optic switches experience losses that affect network function.